Rat renal kallikrein has been purified by 8 M urea hydroxyapapite chromatography of the immune precipitate produced from a kallikrein fraction of low specific activity and specific sheep antiserum. The antibody, uncontaminated by antigen, passed through the column, while the kallikrein was adsorbed and was later eluted by a linera linear phosphate gradient in 3 M KCl. Human renal kallikrein and its specific goat antibody are being purified, by the procedure described above for the rat enzyme, from the immune precipitate formed from 1,500 TAMe units (equivalent to 25 mg of pure enzyme) of partially purified kallikrein and nearly two liters of goat antiserum. In a preliminary experiment, L-arginine attached to agarose via a triazinylaminododecyl arm had an acceptable adsorptive capacity for human renal kallikrein, thus showing promises for use in purification and possibly in separating it from its zymogen.